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Protein kinase C activity of the human myeloma cell line, RPMI 8226, was studied after prepurification on DEAE-cellulose. The total protein kinase activity, eluted at 0.12 M NaCl, was 493 nmol/min/10(10) cells, but 38% was associated with membranes. The lipid dependence of cytosolic and membrane activities was only 52% and 21%, respectively. This activity increased with time, to as much as 200% for the membrane fraction after 7 days, whereas lipid dependence and the PDBu binding properties were lost. This modified activity was not due to the extinction of a copurifying endogenous inhibitor nor to classical PKC proteolysis. TPA-treatment of these cels is accompanied by a rapid, selective and complete loss of lipid-dependent activity of the cytosol, thus benefiting co-migrating lipid independent activity, with no membrane fraction recovery or PKM formation.

We propose a serial assay of both protein kinase C activity and the related [3H]phorbol 12,13-dibutyrate binding, each carried out in 96-multiwell dishes, started and stopped row by row using a multipipet. Protein kinase C activity is observed through the transfer of the gamma-phosphoryl group of radioactive ATP onto histone H1 type III-S. Enzymatic reactions are started by adding enzyme extracts and stopped by adding trichloroacetic acid. Acidic precipitates of each row are simultaneously collected on glass fiber paper using a cell harvester. The addition of bovine serum albumin and cold ATP at the end of the reaction and the addition of trichloroacetic acid in the washing fluid lead to a high recovery of protein kinase C activity and reproducible results. Measurement of [3H]phorbol 12,13-dibutyrate binding to protein kinase C was carried out in a mixed micellar solution as described elsewhere (Y. Hannun and R. M. Bell (1987) in Methods in Enzymology, Vol. 141, pp. 287-293). The quaternary complex formed from protein kinase C, phosphatidylserine, calcium, and [3H]phorbol 12,13-dibutyrate was then bound to a beaded anionic exchanger which was automatically separated from the free phorbol 12,13-dibutyrate by microfiltration using a cell harvester. The binding reaction was highly calcium- and phosphatidylserine-dependent and calcium had to be added to washing fluid for optimal recovery. Determination of protein kinase C activity and phorbol 12,13-dibutyrate binding gave results similar to those of other published methods and the signal/noise ratio was greatly increased. Using a semi-automated cell harvester, the system is partially automated and provides accurate and reproducible results.

L2C B lymphocytes have a constant high DNA synthesis due to their continuous proliferative state. The addition of polymyxin B (PmB), a rather selective inhibitor of protein kinase C, stopped (3H)thymidine incorporation with an IC50 of 10 microM when added 18 h before measuring DNA synthesis. Interestingly, PmB inhibition of DNA synthesis was suppressed when 4 nM 12-O-tetradecanoylphorbol-13-acetate was added along with PmB, indicating that PmB may act through inhibition of protein kinase C. In the node and spleen lymphocytes of normal guinea pigs, protein kinase C activity was entirely cytosolic and was eluted at 0.12 M NaCl when adsorbed on DEAE-cellulose. In L2C leukemic lymphocytes, total protein kinase C activity was of the same order of magnitude, but 20% of it was associated with the membrane fraction. The lipid-dependent activity, eluted at 0.12 M NaCl from cytosolic and membrane fractions, was suppressed by staurosporine with an IC50 of 10-40 nM and by polymyxin B with an IC50 of 2-6 microM. Phosphoinositide metabolism was studied in the transformed cells. Incorporation of 32Pi into polyphosphoinositides was considerable, whereas much more time was required for a tiny incorporation of inositol. We detected no release of radioactive inositol triphosphate. Taken together, these results suggest that protein kinase C function is indispensible for triggering L2C leukemic lymphocyte proliferation. The causes of this permanent activation merit further investigation.